Method to create super secondary grain growth in narrow trenches

ABSTRACT

The present invention relates to a method for obtaining enlarged Cu grains in small trenches. More specifically it related to a method for creating enlarged copper grains or inducing super secondary grain growth in electrochemically deposited copper in narrow trenches and/or vias to be used in semiconductor devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.provisional application Ser. No. 60/790,634, filed Apr. 10, 2006, andclaims the benefit under 35 U.S.C. § 119(a)-(d) of European applicationNo. 06126251.5, filed Dec. 15, 2006, the disclosures of which are herebyexpressly incorporated by reference in their entirety and are herebyexpressly made a portion of this application.

FIELD OF THE INVENTION

The present invention is related to the field of semiconductorprocessing. More specifically it is related to a method for creatingenlarged copper grains or inducing super secondary grain growth inelectrochemically deposited copper in narrow interconnect structures tobe used in semiconductor devices. It further contributes to theexploration of the field of narrow trenches and/or vias in semiconductordevices.

BACKGROUND OF THE INVENTION

Interconnects have been, are, and will continue to be a limiting factorfor the performance and cost of integrated circuits. As technologyscales down further, the problems associated with interconnects becomeever more pressing. The introduction of low-resistive copper as analternative interconnect material for aluminum presents researchers withsome new challenges, since copper cannot be implemented in the samemanner as aluminum alloys.

As feature sizes shrink, narrower copper trenches need to be formed.Also to facilitate closer packing and multilevel connections, trenchesare getting proportionally smaller as they get narrower. These deeptrenches etched into the dielectric must be filled completely, withoutvoids or defects.

Physical Vapor Deposition (PVD) has long time been one of the techniquesof choice for metallization in integrated circuits. In particular,sputter deposition has been widely used in the manufacturing ofhigh-performance on-chip interconnect. However, due to the limitationsof the PVD techniques and the continuing feature sizes it is generallybelieved that the applicability of PVD for the filling of deep trenchesis coming to an end. Sputtering techniques are however widely used todeposit a thin layer of diffusion barrier and/or seed layer in saidfeatures. Unfortunately, PVD suffers from shadowing effects if theaspect ratio of features to be filled is sufficiently large. Saidshadowing effects can form overhanging structures at the top corners ofthe trenches and vias. These effects can lead to void formation whenattempting to fill a feature. Due to the geometrical shadowing, the filmis preferentially deposited on the top corners leading to a “void”within the trench or via.

Electroplated (also referred to as electrochemically deposited or ECD)copper has therefore become the method of choice for filling narrowinterconnect features in the back-end-of-line processing formicroelectronics applications. However, as the trench width decreases,the influence of the PVD deposited seed layer becomes more importantwhen its thickness is not scaled accordingly. This changes the graingrowth dynamics in trenches as the volume fractions of ECD and PVDchange significantly.

Typically copper lines are fabricated by patterning trenches into adielectric layer with optical lithography. A barrier layer and Cu seedare deposited within the trenches, followed by electroplating in orderto fill the structures. A Chemical mechanical polishing (CMP) step isused to remove excess copper and barrier material. A standard hot-plateanneal step (e.g. 30′ at 250° C.) is introduced before CMP to enhancere-crystallization of copper in both seedlayer and plated copper.

The grain growth mechanism in thin PVD copper seed films and in plated(ECD) copper has been described by many authors. Typically, two growthmodes are seen to occur simultaneously, known as normal and secondarygrain growth to those working in the field. The latter leads to grainsizes of several times the thickness of a thin film or width of a trenchand grain boundary motion is erratic. Normally grain growth in theseedlayer is intently retarded through process conditions in order tocreate a stable film for the subsequent ECD process.

Recently, a novel highly concentric grain growth mode, different fromthe commonly observed secondary grain growth (SGG) in ECD copper asdescribed above, referred to as super-secondary-grain-growth (SSGG) hasbeen discovered in thick PVD copper films by Vanstreels et al. Said SSGGwas shown to occur only on alpha-Ta and produce copper grains of manytens of micrometers. In a second stage the SSGG grains initiated in thethick Physical Vapor Deposited (PVD) copper on alpha-Ta were shown toalso be able to recrystallize a bilayer of said layer and an ECD Culayer. In both the ‘PVD-only’ and the ‘PVD-ECD bilayers’ on alpha-Ta,the SSGG and SGG are both active and their rivalry determines the finalgrain structure obtained. It was shown by Vanstreels et al that SSGGdominates at low temperature, but that SGG gains in importance when thetemperature is increased.

Because the SSGG produces [100] oriented super grains of several tens ofmicrometers, less grain boundaries are obtained and hence the resistancein copper having these super grains is lower. This makes the applicationof SSGG in interconnect structures very attractive. There is howeverstill a need to understand the growth mechanisms of said SSGG, and tohave said SSGG lead to large grains in interconnect structures (e.g.trenches) in semiconductor devices. So far, only growth in thin filmshas been demonstrated because the required thickness needed to make SSGGpossible is larger than typical trench dimensions.

SUMMARY OF THE INVENTION

The preferred embodiments relate to a semiconductor device comprising atleast one trench and/or at least one via filled with recrystallizedelectrochemically deposited copper (ECD-Cu), wherein at least 80%, 85%,90%, 91%, or 92% of said recrystallized ECD-Cu consist of copper grainshaving a [100] orientation and dimensions of at least 10 micron.

Preferably, at least 93%, 94%, 95%, 96%, or 97% of said recrystallizedECD-Cu consist of said copper grains having a [100] orientation anddimensions of at least 10 micron.

More preferably, at least 98% or 99% of said recrystallized ECD-Cuconsist of said copper grains having a orientation and dimensions of atleast 10 micron.

Preferably, the dimensions of said copper grains with a [100]orientation are of at least 20 or 25 micrometers.

More preferably, the dimensions of said copper grains with a [100]orientation are of at least 50 micrometers.

Even more preferably, the dimensions of said copper grains with a [100]orientation are of at least 100 micrometers.

Preferably, said trench or trenches have a width of less than 200 nm ina semiconductor device according to the preferred embodiments.

Preferably, said trench(es) has (have) an aspect ratio (or height towidth ratio) higher than 1.

Preferably, a semiconductor device according to the preferredembodiments comprises a diffusion barrier layer (for preventing thecopper diffusion into the layer underneath, more particularly forpreventing the copper diffusion into the dielectric layer underneath)and said recrystallized ECD-Cu upon said diffusion barrier layer.Preferably, said diffusion barrier layer has a thickness of less than 8nm.

Preferably, said diffusion barrier layer is a layer comprising orconsisting of tantalum (Ta), titanium (Ti), ruthenium (Ru), tungsten (W)and/or Manganese (Mn).

Another aspect relates to a method for filling at least one trenchand/or at least one via with copper, comprising the steps of:

-   -   providing said at least one trench and/or said at least one via        by etching an opening in a layer of a dielectric material,    -   depositing or forming a barrier layer (for preventing the copper        diffusion into said dielectric material) in said opening,    -   filling said opening with copper deposited by means of an        electrochemical deposition (or electrochemical plating) process        onto said barrier layer,    -   directly upon said ECD-Cu, depositing a further copper layer by        means of a Physical Vapor Deposition process,    -   performing a thermal treatment for inducing recrystallization        (i.e. for inducing super secondary grains growth) of said        PVD-Cu, whereby recrystallization (i.e. super secondary grains        growth) is also induced into said ECD-Cu (4),    -   removing the copper overburden.

Preferably, in a method according to the preferred embodiments, saidtrench(es) has (have) a width comprised between 50 nm and 200 nm.

Preferably, said trench(es) has (have) an aspect ratio higher than 1.

In a method of the preferred embodiments, before the PVD deposition ofcopper (or inducing layer), said opening can be filled with ECD-Cupartially, substantially or completely. Preferably, said opening iscompletely filled with ECD-Cu.

Preferably, in a method according to the preferred embodiments, saidthermal treatment (also referred to as thermal anneal) is performed at atemperature higher than the relaxation temperature of copper. Moreparticularly, said thermal treatment is performed at a temperaturehigher than 80° C.

Preferably, said thermal treatment is performed at a temperaturecomprised between (about) 100° C. and (about) 420° C., more preferablycomprised between (about) 100° C. and (about) 400° C., more particularlycan be performed at (about) 130° C., and even more preferably at about200° C.

Preferably, in a method according to the preferred embodiments, asubstrate bias of 250 W is applied during said PVD deposition step fordepositing said PVD-Cu.

Preferably, said thermal treatment is performed for at least 30 minutes,more preferably for at least 1 hour, and even more preferably for atleast 1.5 hour.

Preferably, in a method according to the preferred embodiments, thethickness of the PVD-Cu layer (5) is comprised between 400 nm and 1000nm, and more particularly is about 500 nm.

Preferably, in a method according to the preferred embodiments, saidbarrier layer can comprise or consist of tantalum (Ta), titanium (Ti),ruthenium (Ru), tungsten (W) and/or Manganese (Mn). Preferably, saidbarrier layer comprises or consists of α-Ta, β-Ta or TaN.

A method according to the preferred embodiments can further comprise,before the step of depositing said ECD-Cu, the step of depositing acopper seedlayer onto said barrier layer, preferably by means of aPhysical Vapor Deposition process.

A method according to the preferred embodiments can further comprise,before the step of depositing said PVD-Cu, the step of removing theoverburden of ECD-Cu and seedlayer, using said barrier layer as astopping layer.

Said removal step of said overburden of ECD-Cu and seedlayer can beperformed by chemical mechanical polishing (CMP).

Alternatively, in a method according to the preferred embodiments, Mncan be incorporated into a copper seedlayer (the Mn being incorporatedduring the step of depositing said copper seedlayer by Physical VaporDeposition), and said Mn-containing-seedlayer is then submitted to athermal treatment that causes the movement of the Mn towards thedielectric material such that the Mn-containing-seedlayer can act as abarrier layer. The deposition of a barrier layer prior to the depositionof said Mn-containing-seedlayer becomes then needless.

In a method according to the preferred embodiments wherein no seedlayeris deposited, the overburden of ECD-Cu (if any) can be removed by a wetand/or dry etchback process.

In a method according to the preferred embodiments the overburden ofPVD-Cu and the overburden of barrier layer (if any or if remaining) canbe removed by chemical mechanical polishing (CMP). Said removal can alsobe performed by dry and/or wet etchback.

In a method according to the preferred embodiments, Mn can beincorporated in said ECD-Cu for migrating, during said thermal treatmentstep (for recrystallization of both ECD-Cu and PVD-Cu), towards saiddielectric layer, to act as barrier layer.

By adjusting the different parameters inherent to a method according tothe preferred embodiments, and more particularly by adjusting thetemperature during the thermal treatment, the thickness of ECD-Cu, thethickness of PVD-Cu, and/or the substrate bias applied, more than 80%,or more than 93%, and even more than 98% or 99% (all the values, integeror real number, between 80% and 99% being envisaged) of saidrecrystallized ECD-Cu can consist of copper grains with a [100 ]orientation having dimensions of at least 10 micron, of at least 20 or25 micron or of at least 100 micron.

A method according to the preferred embodiments can be used in theframework of a damascene method or of a dual damascene method forforming an interconnect.

Another aspect relates to a semiconductor device obtainable by a methodaccording to the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

All figures/drawings are intended to illustrate some aspects andembodiments of the present invention. Devices are depicted in asimplified way for reason of clarity. Not all alternatives and optionsare shown and therefore the invention is not limited to the content ofthe given drawings. Like numerals are employed to reference like partsin the different figures.

FIGS. 1A to 1F (PRIOR ART) illustrate the formation of conductivestructures (e.g. trenches) and subsequent filling and recrystallizationof copper within the trenches according to state of the art techniques.

FIGS. 2A to 2I illustrate the preferred embodiment for formation andfilling of narrow trenches (or vias) with electroplated copper (ECD-Cu)and subsequent recrystallization of the copper according to the methodof the preferred embodiments to form (or to obtain) Super SecondaryGrain Growth (SSGG) in said ECD-Cu.

FIGS. 3A to 3I illustrate an alternative and also preferred embodimentfor formation and filling of narrow trenches (or vias) using directplating of copper onto a resistive barrier layer and subsequentrecrystallization of the copper according to the method of the preferredembodiments to form (or to obtain) Super Secondary Grain Growth (SSGG)in said ECD-Cu.

FIGS. 4A to 4H illustrate an alternative and also preferred embodimentfor formation and filling of narrow trenches (or vias) usingelectroplated copper. Said electroplated copper has a very thinoverburden such that an extra planarizing step can be skipped.Subsequent recrystallization of the electroplated copper according tothe method of the preferred embodiments leads to Super Secondary GrainGrowth (SSGG) in said ECD-Cu.

FIG. 5 illustrates super secondary grains in a 500 nm thick PVD filmdeposited at 250 W and annealed at 250° C. for 1 hour (scalebar=500 μm).

FIG. 6 illustrates the stress in ECD deposited copper as a function ofthe (annealing) temperature indicating the temperature range for growthof supergrains according to the method of the preferred embodiments.

FIG. 7( a) illustrates the distribution of crystallographic orientationsas observed in ECD deposited copper having the original [111]crystallographic orientation (texture). FIG. 7( b) represents a grainstructure where both SGG and SSGG grains are present. For the conditionwhere SSGG is most complete as shown in FIG. 7( c) the original [111]texture of the as-deposited film has disappeared completely (afterperforming the method of the preferred embodiments).

FIG. 8 illustrates standard resistivity values for Cu trenches (i.e.without carrying out the method according to the preferred embodiments)as a function of the cross-sectional area of the trench (trenchheight=130 nm).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings described are only schematic and are non-limiting. In thedrawings, the size of some of the elements may be exaggerated and notdrawn on scale for illustrative purposes. The dimensions and therelative dimensions do not correspond to actual reductions to practiceof the invention.

In the context of the preferred embodiments, the term “ElectrochemicalDeposition” (ECD), also referred to as Electro Chemical Plating (ECP),refers to the process used to fill trenches and/or vias with copper toform interconnects structures on a wafer substrate. The ECD process isthe process of depositing a metal (copper) by means of electrolysis andinvolves placing the wafer substrate in an aqueous electrolytecontaining metal ions (e.g. Cu(II) ions).

The term “seedlayer” as referred to in this application is a layer usedto provide a conductive path for the electric current that is requiredto electroplate copper. As such, an underlying conductive seed layer isgenerally applied to the wafer before it is subjected to anelectrochemical deposition process. PVD is the preferred applicationprocess for the conductive seed layer because it can readily depositcopper on the barrier layer with relatively good adhesion.

The term “direct plating” refers to Electrochemical Deposition (ECD) orElectro Chemical Plating (ECP) using highly resistive barrier layerssuch that no seedlayer is needed and direct plating onto the barrierlayer is possible.

The orientation of the secondary grains and/or of the super secondarygrains is expressed as a direction [xyz] parallel to the substrate.Super secondary grains have a [100] orientated growth while secondarygrains have a [111] orientated growth.

In the context of the preferred embodiments, the term “aspect ratio”refers to the ratio of the height dimension to the width dimension ofparticular openings into which an electrical contact is to be placed.For example, a via opening which typically extends in a tubular formthrough multiple layers has a height and a diameter, and the aspectratio would be the height of the tubular divided by the diameter. Theaspect ratio of a trench would be the height of the trench divided bythe minimal travel width of the trench at its base.

Furthermore, the term “anneal” as used in the description refers to aheat treatment to which a wafer is subjected in order to modifyproperties of materials or structures processed on its surface or in thebulk.

The preferred embodiments provide a method for creation of supersecondary grains in narrow conductive structures such as trenches andvias in a semiconductor device.

The method of the preferred embodiments is suitable for filling of anopening (a trench and/or a via) to form interconnect structure, e.g. asingle damascene structure (SD) or a dual damascene structure (DD), withSSG.

A method is disclosed for filling trenches and/or vias for formingcopper interconnect structures in a semiconductor device, said copperbeing characterized as recrystallized electrochemically deposited copperand having enlarged copper grains with a [100] orientation.

Said enlarged copper grains, also referred to as super secondary grains(SSG), result from the recrystallization of ECD-Cu, saidrecrystallization of said ECD-Cu being induced by the recrystallizationinitiated into a PVD deposited copper layer (PVD-Cu) contacting andbeing situated on top of said ECD-Cu.

Into said PVD deposited copper layer (PVD-Cu), super secondary grainsare induced, said super secondary grains grow (expand) further into theelectrochemically filled copper trench.

The preferred embodiments are based on the surprising discovery that thesuper secondary grains (SSG) after being induced in a PVD-Cu layer growfurther into electrochemically filled copper trench, saidelectrochemically filled copper trench being situated underneath and indirect contact with said PVD-Cu layer. Indeed, said SSG cannot beobtained by annealing an ECD-Cu layer that is not into direct contactwith a PVD-Cu layer.

The initially concentric growth of the super secondary grains in saidPVD-Cu layer continues in other directions (towards and into theinterconnect structure) and seems not hampered when it is limited in onedirection.

More specifically a method is disclosed to create (to allow) supersecondary grain growth within narrow interconnect structures (trenchesand/or vias) in semiconductor devices, said super secondary grainshaving a [100] oriented structure and a length of several tens ofmicrons; said interconnect structures being preferably part of a singleor dual damascene structure.

The method of the preferred embodiments provides processing steps tocreate narrow trenches and/or vias filled with low resistivity copperbeing characterized as having super secondary grains. RecrystallizedECD-Cu according to a method of the preferred embodiments exhibits lowerresistivity than ECD-Cu obtained by standard methods.

The processing preferably starts with first etching an opening (trenchor via) in a dielectric layer.

Said dielectric layer can be any suitable material to be used asdielectric material in semiconductor processing. Preferably, saiddielectric layer is a low-k dielectric material (i.e. a dielectricmaterial having a dielectric constant lower than that of SiO₂).

If the opening is a trench, said trench opening preferably has a widthof less than 200 nm and an aspect ratio of more than unity.

Preferably, subsequently, a copper diffusion barrier layer is depositedin said opening.

Said barrier layer is preferably a thin tantalum (Ta) comprising layerdeposited by Physical Vapor Deposition (PVD) or atomic layer deposition(ALD).

Most preferred, but not limited to, said Ta comprising barrier layer isan α-Ta, β-Ta or TaN comprising layer.

Said barrier layer can be an α-Ta, β-Ta or TaN layer.

The barrier layer has preferably a thickness of less than 8 nm and morepreferred has a thickness of less than 10% of the trench width.

Other (bi-)layers that act as a copper diffusion barrier (e.g. WCN, andTa(N)/Ru) can also be considered.

To perform electrochemical plating onto said barrier layer, a thincopper seedlayer can be deposited, said seedlayer is preferablydeposited by PVD.

Direct plating can also be performed, for which there is no need todeposit a copper seedlayer onto the barrier layer. Direct plating useshighly resistive barrier layers such that no seedlayer is needed anddirect plating onto the barrier layer is possible.

The remaining part of the trench opening is then filled withelectrochemically plated copper (ECD-Cu). Said opening can be partiallyfilled, substantially filled or completely filled. Preferably, theopening is completely filled.

The overburden of ECD-Cu and (optionally) of PVD-Cu seedlayer (if any)can be removed (from the field area) using the barrier layer (on thefield) as a stopping layer.

The removal process is preferably a chemical mechanical polishing step.Alternatively a wet or dry etchback process can be used.

A second thick copper layer (preferably thicker than the ECD-Cu layer),further referred to as inducing layer is deposited onto the planarizedsurface by Physical Vapor Deposition (PVD-Cu) using a high bias.

Said high bias is preferably higher than 150 W. More preferred said biasis at least 250 W for a 200 mm wafer. The optimal bias setting for a 300mm wafer is thus higher.

The thickness of said second PVD-Cu layer or inducing layer ispreferably in the range of 400 nm to 1000 nm and most preferred 500 nm.

A thermal anneal is performed to induce super secondary grain growth inthe thick PVD-Cu inducing layer. Then said super secondary grainsfurther “migrate” (or grow, or expand) further into the ECD-Cu such thatlower resistivity copper having super secondary grains (SSG) isobtained.

The expansion process has to be understood as a process during which theinduced SSG keep on growing such that they grow further into the narrowstructures filled with ECD-Cu, such that said SSG substantially fillsaid narrow structures.

The thermal anneal is performed at temperatures above the relaxationtemperature of copper. Said relaxation temperature is about 80° C. Saidthermal anneal can be performed at temperatures in the range of 80° C.up to 120° C. Preferably, said thermal anneal is performed attemperatures in the range of 100° C. up to 420° C., more preferably inthe range of 100° C. up to 400° C. and even more preferably around 200°C.

After completion of the SSGG process and formation of SSG in the ECD-Custructure, the overburden of the second PVD-Cu inducing layer isremoved.

The removal is preferably performed by chemical mechanical polishing(CMP) or alternatively by a wet and/or dry etchback process.

The barrier layer on the field can be removed subsequently to theremoval of the inducing layer.

Alternatively, when using an ECD process that produces a very thinoverburden, the PVD copper inducing layer can be deposited directly ontop of this ECD layer without the intermediate CMP step. And the finalCMP step removes the PVD inducing layer, barrier layer, seedlayer (ifany) and ECD-Cu on the field.

In another alternative, the barrier step can be skipped and a seedlayercomprising Mn can be deposited before ECD. This Mn solute then forms abarrier layer during the thermal anneal step.

Alternatively, Mn can be incorporated in ECD-Cu during plating. Said Mnthen migrates during a thermal anneal towards the dielectric and actthere as a barrier.

The preferred embodiments also relate to a semiconductor device havingat least one interconnect structure filled with (recrystallized)electrochemically deposited copper (ECD-Cu), said ECD-Cu is furthercharacterized as low resistivity copper and having super secondarycopper grains (SSG). Said SSG have a [100] orientation.

More specifically, more than 80% of said recrystallized ECD copper arein the form of SSG with a [100] orientation.

Preferably, more than 93% of said recrystallized ECD copper are in theform of SSG with a [100] orientation.

More preferably, more than 98% of said recrystallized ECD copper are inthe form of SSG with a [100] orientation.

Making such a strong oriented copper structure is an advantage for theelectro-migration of the copper.

Said SSG are further characterized as having dimensions of at least 10micron. Preferably, said SSG have dimensions of at least 20 micron, ofat least 25 micron, of at least 50 micron, and more preferably of atleast 100 micron.

Said SSG grains are first formed in a PVD-Cu inducing layer which isinto contact with said ECD-Cu and said SSG grains “migrating” (orgrowing, or expanding) further in said ECD-Cu. The PVD-Cu layer ispreferably removed after “migration” (or growth, or expansion) of theSSG into the ECD-Cu.

Interconnect structures made of copper having enlarged copper grainshave improved resistivity due to a decrease of the number of grainboundaries per unit volume.

Said enlarged copper grains have preferably a dimension of at least 10micron (μm), more preferred more than 25 micron (μm) and most preferredmore than 100 micron (μm), whereas the conventional secondary coppergrains as obtained after an anneal of ECD-Cu have dimensions of 1-2microns (μm).

The copper used in a method or a semiconductor device according to thepreferred embodiments preferably includes alloys of copper of the kindtypically used in the semiconductor industry. More preferably, andaccording to preferred embodiments, a copper alloy comprising about 98%by weight of copper is used.

A method according to a preferred embodiment is illustrated in FIGS. 2Ato 2H.

A method of the preferred embodiments solves the problem of fillingtrenches having aspect ratios greater than 1 for forming interconnectstructures without voids and with low resistivity copper.

Physical Vapor Deposition (PVD) of copper gives rise to a more densedeposited copper layer compared to an Electrochemical deposited (ECD)copper layer but filling said trenches with PVD is however not wantedbecause this technique leads to void formation in shallow structures.

On the other hand, ECD is known as a technique capable of perfectbottom-up fill of narrow features.

It is further known that stress in a PVD deposited copper can be tunedduring the deposition process by tuning the substrate bias, leading toan excess (e.g. more than 80%) of the more preferred [100] orientationof the copper such that growth of super secondary copper grains (SSG) ispossible.

Unexpectedly, the preferred embodiments combine the benefits of bothtechniques for filling trenches and/or vias for forming interconnectstructures or in other words makes the growth of SSG possible withinsaid trenches and/or vias filled with ECD copper.

The formation of SSG in narrow trenches (and/or vias) is disclosed.

Said super secondary grains (SSG) have a [100] oriented structure and alength of several tens of microns. Said enlarged copper grains havepreferably dimension of at least 10 micron (μm), more preferred morethan 25 micron (μm) and most preferred more than 100 micron (μm) whereasthe conventional secondary copper grains as obtained after an anneal ofECD-Cu have dimensions of 1-2 microns (μm).

After applying a method of the preferred embodiments, more than 80% ofsaid ECD copper has a [100] orientation (in the form of SSG), morepreferred more than 93% of said ECD copper has a [100] orientation andmost preferred 98% of said ECD copper has a [100] orientation.

Making such a strong oriented copper structure is an advantage for theelectro-migration of the copper.

Said SSGG are created in ECD-Cu by first inducing super secondary grainsin an inducing layer covering the top of said ECD-Cu structure. Saidinducing layer is a PVD deposited copper (containing) layer.

A method according to the preferred embodiments comprises the steps offirst creating an opening (i.e. trench or via) for forming aninterconnect structure in a substrate.

Said substrate is preferably a semiconductor wafer comprising activedevices with on top of said substrate a dielectric layer 1 such as SiO₂,or a low-k dielectric such as CVD deposited SiCOH materials (e.g. BlackDiamond®), or organic spin-on materials (e.g. Silk®), etc.

Photolithographic patterning followed by reactive ion etching is used toperform the etching of the opening (trench or via) in said dielectriclayer 1.

If the opening is a trench, said trench opening preferably has a widthof less than 200 nm and an aspect ratio of more than unity.

Subsequently a continuous barrier layer 2 is deposited onto saiddielectric layer 1, said barrier layer 2 is deposited as a continuouslayer onto the sidewalls and bottom of the opening as well as onto theupper part of the dielectric layer (also referred to as overburden).

Said copper diffusion barrier layer 2 can be a Ta comprising layer suchas α-Ta (crystalline), β-Ta (crystalline) or a TaN (amorphous) layer.

Other state of the art copper diffusion barrier layers are alsopossible; examples are Ti comprising layers (e.g. TiN/Ti), W comprisinglayers (e.g. WCN), Ru comprising layers, etc.

The barrier layer 2 is preferably deposited by Physical Vapor Deposition(PVD) or Atomic Layer Deposition (ALD). Said PVD deposited layer haspreferably a thickness lower than 8 nm. Preferably the thickness of thebarrier layer 2 is less than 10% of the trench width.

In a preferred embodiment, onto the barrier layer, a seedlayer 3 can bedeposited. Said seedlayer 3 is preferably characterized as a PVDdeposited copper layer with thickness in the range of preferably 10 nmup to 70 nm and more preferred around 30 nm. Said seed layer 3 isdeposited uniformly on top of the previously deposited barrier layer 2.Most preferred the sidewalls of the opening are covered completely by aseedlayer 3. The seedlayer 3 provides a conductive path for theelectrochemical plating afterwards.

After deposition of the seedlayer 3, the substrate is immersed in aplating solution such that copper from the plating bath can beelectrochemically deposited onto the seed layer. A complete filling ofthe opening (trench or via) with ECD-Cu 4 can be obtained. As a sideeffect, an overburden of copper is present on the field area.

Depending on the thickness of the ECD-Cu overburden, the overburden(ECD-Cu) is then removed by means of chemical mechanical polishing (CMP)or etchback.

The barrier layer 2 present on the field can serve as a stopping layerfor etchback or CMP as illustrated in FIG. 2F.

As shown in FIG. 2G, a thick copper layer is deposited onto saidplanarized surface, said copper layer is a PVD deposited copper layerusing a high bias during deposition.

Said high bias setting can be tool specific. A preferred bias is higherthan 150 Watt and more preferred around 250 W for a 200 mm wafer.

The optimal bias setting for a 300 mm wafer will be higher than for a200 mm wafer.

Said thick PVD-Cu layer 5 is further referred to in this application asan inducing layer.

The thickness of the PVD-Cu inducing layer 5 is preferably in the rangeof 400 to 1000 nm and most preferred around 500 nm.

The PVD-Cu layer is also characterized as a layer having a high stress(due to the high substrate bias applied during deposition).

Recently developed PVD deposition techniques such as Ion Metal Plasma(IMP) and Self Ionized Plasma (SIP) deposition are also envisaged.

Subsequently, a thermal treatment or thermal anneal is performed suchthat a recrystallization within the PVD-Cu inducing layer 9 is achieved.

The period of time between the deposition of the inducing layer (PVD-Cu)and the thermal anneal is preferably as short as possible.

Most preferred the thermal anneal is performed at temperatures justabove the relaxation temperature of copper, said relaxation temperatureof copper being in the range of 80° C. up to 120° C.

Said anneal temperature is preferably in the range of 100° C. up to 420°C., and more preferably between 100° C. and 400° C. More particularly,said anneal temperature is around 130° C. and more preferably about 200°C.

FIG. 6 illustrates the stress release within the PVD-Cu layer as afunction of the anneal temperature.

The optimal temperature range for the thermal anneal of the preferredembodiments during which stress relaxation is achieved and SSG growth isoptimal is indicated.

During the thermal anneal, SSG are induced in said inducing layer(PVD-Cu) and said SSG expand further into the ECD-Cu underneath.

Said thermal anneal step is preferably performed during 0.5 hour (30minutes) minimum, preferably during more than 1 hour and most preferredaround 1.5 hour.

A minimum anneal time is necessary for generating and expanding saidSSGG, and can be adjusted in function of different parameter and inparticular in function of the bias applied, of the thickness of theECD-Cu and PVD-Cu layers, or of the percentage of copper grains with an[100] orientation and with dimensions higher than 10, 25 or 100 μmenvisaged.

During said thermal anneal, super secondary grain growth (SSGG) isinduced in said PVD-Cu inducing layer 9.

Said SSGG leads to the formation of super secondary grains (SSG) havinga [100] orientation and grains sizes of at least several tens ofmicrometers. The SSG have a grain growth rate of approximately 100μm/hour.

The optimal time of the thermal anneal to transform the ECD-Cu (creatingmore than 80% SSG in said ECD-Cu) is further dependent on the chemistry(plating bath composition) used to deposit the ECD-Cu.

Said SSG are characterized as having low resistivity and improvedelectro-migration, and due to their (large) size there are very fewgrain boundaries. Said SSG continue growing into the ECD-Cu underneathsuch that the opening is at least partly filled with SSG 6.

After thermal anneal, the PVD-Cu inducing layer 9 and barrier layer 5are removed.

Removal is preferably achieved by means of Chemical Mechanical Polishingor alternatively by wet and/or dry etchback techniques.

In an alternative and also preferred embodiment, direct plating ontohighly resistive barrier layers is used as technique to fill the openingelectrochemically with copper.

This alternative is schematically shown in FIGS. 3A to 3I, having directplated ECD-Cu 8 onto the barrier layer in the opening.

This alternative makes the step of depositing a seedlayer onto thebarrier layer needless.

Said highly resistive barrier layer can be a TiN/Ti layer or a TaNlayer.

Alternatively, a thin layer or clusters of a noble metal (e.g. Pt, Pd,or Ru) can be deposited onto the barrier layer to favor the directplating process.

In yet another alternative and also preferred embodiment,electrochemical deposition of copper is optimized such that only a verythin overburden of ECD-Cu is formed onto the field area.

This makes the step of removing the ECD-Cu (e.g. by means of CMP) on thefield needless.

A final CMP step removes the PVD-Cu inducing layer as well as theseedlayer and ECD-Cu on the field. This alternative is schematicallyshown in FIGS. 4A to 4H.

In yet another alternative and also preferred embodiment, a barrierlayer deposition can be skipped and Mn can be incorporated in copper(e.g. an alloy of Mn and Cu, e.g. wherein Mn represents 5 w. % to 15 w.% of the alloy and copper the complement) during deposition of copper.

Mn can be e.g. incorporated in the Cu seedlayer during seedlayerdeposition onto the sidewalls of and the bottom of the (via or trench)opening.

Alternatively Mn can be incorporated into the ECD-Cu during theelectrochemical plating process.

During the thermal anneal as described in previous embodiments to induceSSGG, Mn migrates towards the dielectric material and act as barrier.

This alternative is extremely useful in dual damascene processing tocreate self-aligned barrier layers in the dual damascene structure(leading to direct Cu—Cu contact).

All references cited herein, including but not limited to published andunpublished applications, patents, and literature references, areincorporated herein by reference in their entirety and are hereby made apart of this specification. To the extent publications and patents orpatent applications incorporated by reference contradict the disclosurecontained in the specification, the specification is intended tosupersede and/or take precedence over any such contradictory material.

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps.

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification are to be understood as beingmodified in all instances by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth herein areapproximations that may vary depending upon the desired propertiessought to be obtained. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of anyclaims in any application claiming priority to the present application,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches.

The above description discloses several methods and materials of thepresent invention. This invention is susceptible to modifications in themethods and materials, as well as alterations in the fabrication methodsand equipment. Such modifications will become apparent to those skilledin the art from a consideration of this disclosure or practice of theinvention disclosed herein. Consequently, it is not intended that thisinvention be limited to the specific embodiments disclosed herein, butthat it cover all modifications and alternatives coming within the truescope and spirit of the invention.

1. A method for filling a structure with copper, the method comprising the steps of: etching an opening in a layer of a dielectric material, whereby a structure selected from the group consisting of a trench and a via is formed; depositing or forming a barrier layer in said opening for preventing copper diffusion into said dielectric material; filling said opening by depositing copper in an electrochemical deposition or electrochemical plating process onto said barrier layer; depositing a further copper layer by physical vapor deposition directly upon said electrochemically deposited copper; performing a thermal treatment for inducing recrystallization of said physical vapor deposition deposited copper, whereby recrystallization is also induced in said electrochemically deposited copper; and removing a copper overburden.
 2. The method according to claim 1, wherein said structure is a trench, and wherein said trench has a width of from 50 nm to 200 nm.
 3. The method according to claim 2, wherein said trench has an aspect ratio higher than
 1. 4. The method according to claim 1, wherein said thermal treatment is performed at a temperature of from about 100° C. to about 420° C.
 5. A method according claim 1, wherein said thermal treatment is performed at a temperature of about 200° C.
 6. The method according to claim 1, wherein a substrate bias of 250W is applied during said physical vapor deposition step for depositing said physical vapor deposition deposited copper.
 7. The method according to claim 1, wherein said thermal treatment is performed for at least 30 minutes.
 8. The method according to claim 1, wherein the thickness of the further copper layer is from 400 nm to 1000 nm.
 9. The method according to claim 1, wherein said barrier layer comprises a metal selected from the group consisting of tantalum, titanium, ruthenium, tungsten, manganese, and combinations thereof.
 10. The method according to claim 1, wherein said barrier layer comprises a material selected from the group consisting of α-tantalum, β-tantalum, tantalum nitride, and combinations thereof.
 11. The method according to claim 1 further comprising, before the step of depositing said electrochemically deposited copper, the step of depositing a copper seedlayer onto said barrier layer by physical vapor deposition.
 12. The method according to claim 1, wherein said barrier layer is formed by, first, incorporating manganese in a copper seedlayer during the deposition of said copper seedlayer by physical vapor deposition, and then annealing said manganese-containing seedlayer.
 13. The method according to claim 1 further comprising, before the step of depositing said physical vapor deposition deposited copper, a step of removing an overburden of electrochemically deposited copper.
 14. The method according to claim 11, further comprising a step of removing an overburden of said copper seedlayer, wherein said step is conducted before the step of depositing said physical vapor deposition deposited copper, during a step of removing an overburden of electrochemically deposited copper using said barrier layer as a stopping layer.
 15. The method according to claim 13, wherein said step of removing an overburden of electrochemically deposited copper is performed by chemical mechanical polishing.
 16. The method according to claim 14, wherein said step of removing an overburden of said copper seedlayer is performed by chemical mechanical polishing.
 17. The method according to claim 1 further comprising a step of removing an overburden of physical vapor deposition deposited copper and an overburden of barrier layer.
 18. The method according to claim 17, wherein said step of removing an overburden of physical vapor deposition deposited copper and an overburden of barrier layer is performed by chemical mechanical polishing.
 19. The method according to claim 17, wherein said step of removing said overburden of physical vapor deposition deposited copper and an overburden of barrier layer is performed by at least one of a dry etchback and a wet etchback.
 20. The method according to claim 1, wherein manganese is incorporated in said electrochemically deposited copper, wherein the manganese migrates, during said thermal treatment step, towards said dielectric layer to act as barrier layer.
 21. The method according to claim 1, whereby at least 80% of said recrystallized electrochemically deposited copper consist of copper grains with a [100] orientation and dimensions of at least 10 microns.
 22. The method according to claim 1, whereby at least 93% of said recrystallized electrochemically deposited copper consist of copper grains with a [100] orientation and dimensions of at least 10 microns.
 23. The method according to claim 1, whereby at least 98% of said recrystallized electrochemically deposited copper consist of copper grains with a [100] orientation and dimensions of at least 10 microns.
 24. A damascene method for forming an interconnect comprising the method according to claim
 1. 25. A dual damascene method for forming an interconnect comprising the method according to claim
 1. 26. A semiconductor device obtainable by the method according to claim
 1. 